Transistorized Ignition
Hello, I am rebuilding a 1966 427/425 transistor distributor and want to reduce the total centrifugal advance. Does GM offer a pole piece other than the 536 ( part # 1967928), that is currently in this unit? I know I can weld the advance slot, however I would rather install a correct part if available. I want to run an initial advance of 10 to 12 degrees, and would like to limit my total initial plus mechanical advance to 38 to 40 degrees. That would mean I need a 526 or 528 pole piece. Are these available from GM or any other supplier? I am installing a B26 vacuum advance unit and will be running manifold (direct) and not ported vacuum. Thanks in advance for any and all help, John
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Re: Transistorized Ignition
John, No GM does not offer a pole piece. I have two NOS 1967928 in unopened boxes. But I know that this part is a service replacement. Like yours.
John D. -
Re: Transistorized Ignition
I recommend AGAINST reducing the total centrifugal advance on big blocks. There is a reason why most have 30-32 centrifugal and recommended single digit initial timing.
The early closed chamber big block heads with two large quench zones don't like as much low speed, low load advance as small blocks or later open chamber big block heads. Too much low speed, low load advance can lead to "trailer hitching" - that fore-aft jerking motion.
L-72 centrifugal of 30 degrees isn't all in until 5000, which is very lazy. The '67 L-71 has it all in at 3800 and this carried through to '69.
The first thing you need to do is check where the centrifugal comes in and what's the total. There's a good chance that it's been modified somewhere along the way, hopefully for the better, but maybe for the worse.
If it's still OE get a Mr. Gasket 928G spring kit. The springs, lightest to heaviest, are black - silver - gold. Set initial at 8-10 then find the spring combination that gets full centrifugal in as soon as possible WITHOUT detonation, which is the limiting factor.
If the cam is OE equivalent it should pull at least 14" at 900 with full time vacuum advance, so a 12" B26 VAC passes the Two-Inch Rule.
DukeComment
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